From: Ross Zwisler Subject: Re: [PATCH 2/2] ext2: Add locking for DAX faults Date: Tue, 13 Oct 2015 09:02:45 -0600 Message-ID: <20151013150245.GA22694@linux.intel.com> References: <1444428128-12200-1-git-send-email-ross.zwisler@linux.intel.com> <1444428128-12200-3-git-send-email-ross.zwisler@linux.intel.com> <20151011231443.GY27164@dastard> <20151012214135.GA24720@linux.intel.com> <20151012232427.GH27164@dastard> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Ross Zwisler , linux-kernel@vger.kernel.org, Jan Kara , linux-ext4@vger.kernel.org, Dan Williams , linux-nvdimm@lists.01.org, Matthew Wilcox , Andreas Dilger To: Dave Chinner Return-path: Content-Disposition: inline In-Reply-To: <20151012232427.GH27164@dastard> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Tue, Oct 13, 2015 at 10:24:28AM +1100, Dave Chinner wrote: > On Mon, Oct 12, 2015 at 03:41:35PM -0600, Ross Zwisler wrote: > > On Mon, Oct 12, 2015 at 10:14:43AM +1100, Dave Chinner wrote: > > > On Fri, Oct 09, 2015 at 04:02:08PM -0600, Ross Zwisler wrote: > > > > Add locking to ensure that DAX faults are isolated from ext2 operations > > > > that modify the data blocks allocation for an inode. This is intended to > > > > be analogous to the work being done in XFS by Dave Chinner: > > > > > > > > http://www.spinics.net/lists/linux-fsdevel/msg90260.html > > > > > > > > Compared with XFS the ext2 case is greatly simplified by the fact that ext2 > > > > already allocates and zeros new blocks before they are returned as part of > > > > ext2_get_block(), so DAX doesn't need to worry about getting unmapped or > > > > unwritten buffer heads. > > > > > > > > This means that the only work we need to do in ext2 is to isolate the DAX > > > > faults from inode block allocation changes. I believe this just means that > > > > we need to isolate the DAX faults from truncate operations. > > > > > > Why limit this just to DAX page faults? > > > > Yep, I see that XFS uses the same locking to protect both DAX and non-DAX > > faults. I'll add this protection to non-DAX ext2 faults as well. > > > > One quick question - it looks like that dax_pmd_fault() only grabs the > > pagefault lock and updates the file_update_time() if the FAULT_WRITE_FLAG is > > set. In xfs_filemap_pfn_mkwrite(), though, these two steps are taken for read > > faults as well. Is this intentional? > > xfs_filemap_pfn_mkwrite() should not be called for read faults. > We've already had to have a fault that maps the page to pfn for us > to get a pfn based fault, and hence that code is correct. > > Or are you talking about xfs_filemap_pmd_fault()? In which case, I > refer you to the commit log and it should be obvious that it was > committed without me even looking at it. I have another patch in my > current series for 4.4 that will fix this. Yep, sorry, I meant xfs_filemap_pmd_fault(). Thanks, I was just making sure the pattern I'm following in ext2 where I'm only locking the pagefault lock & updating the file_update_time() on writes was correct.